Speech server application and Cache

In the speech server application I am creating, I need to load some data and save it into the Cache so every call can share that data in a readonly fashion. The normal way for me to access Cache is to use HttpContext.Current.Cache. However, HttpContext.Current is null in speech server application. I tested in both IIS 5.1 and 6.0 with soft and regular land phone. I then began to use WorkFlow.UserData as the application Cache. It works fine except you can't set its expiration time. After a little research and I found that I can acutally access Cache by HttpRuntime.Cache, and it even performance a little better. A good article to compare these two different way of accessing Cache is here.